This invention relates to a connecting rod and more particularly to an improved connecting rod arrangement that can be utilized with internal combustion engines or other similar reciprocating machines.
As is well known, reciprocating machines employ one or more pistons that are connected by means of connecting rods to a crankshaft for transmitting motion therebetween. If the mechanism operates as an engine, the piston drives the crankshaft through the connecting rod. If, on the other hand, the machine is a compressor, then the crankshaft drives the piston through the connecting rod. However, the construction of the connections between the piston, connecting rod, and crankshaft are generally the same.
In one typical connection type, the connecting rod has its small end formed with a bearing that receives a piston pin for providing the pivotal connection to the piston. The opposite or big end of the connecting rod has a crankshaft bearing that extends parallel to the piston pin bearing of the small end.
With many types of arrangements, the big end of the connecting rod is split into a main portion and a bearing cap portion that are affixed to each other by means of a pair of threaded fasteners. These threaded fasteners lie on an axis that defines a plane that extends perpendicularly to the plane of the axes of the bearing portions of the big and small ends.
Typically, the plane defined by the fasteners bisects the small end bearing. However, this type of arrangement provides certain disadvantages, particularly with connecting rod structures where the center of gravity of the connecting rod may not lie on the same plane as that which contains the axes of the threaded fasteners.
This type of arrangement can be understood by reference to FIG. 1, which is a side elevational view of a connecting rod, piston, crankshaft connection, and wherein the cylinder is shown partially in cross section and FIG. 2 which is a schematic partially schematic view showing the angular relationships of the cylinder bores of the cylinder block.
In FIG. 1 the reciprocating machine is of the type having a pair of angularly disposed cylinder banks the cylinder bores of which are shown schematically at 14a in FIG. 2. As is typical with this type of machine, be it an engine or a compressor, a crankshaft, indicated by the reference numeral 11, is provided with a single journal portion between a pair of cheeks 12 on which two connecting rods 13 are journaled in side-by-side fashion. The rotational axis 11a of the crankshaft is indicated in FIG. 2. Although the invention is described in conjunction with such a type of mechanism, it will be readily apparent to those skilled in the art that the inventive features can be used with engines having other cylinder configurations and in-line engines. Also, the invention is described in conjunction with only a single cylinder of the engine, but it will be apparent to those skilled in the art how it is employed with multiple cylinder machines.
The machine is provided with a cylinder block 14 in which a cylinder bore 15 is formed by a pressed or cast-in liner 16. A piston 17 is supported for reciprocation within the cylinder bore 15.
The connecting rod 13 has an upper or small end 18 that defines a piston pin bore which extends in a plane parallel to the plane of FIG. 1 and which receives a piston pin 19 that extends through a pair of pin bosses 21 of the piston 17 to provide a pivotal connection at this end. A pair of thrust washers 22 may be positioned between the sides of the small end 18 and the pin bosses 21.
The lower or big end of the connecting rod 13 is indicated generally by the reference numeral 23, and this is split into an upper portion 24 which is integral with the connecting rod portion 13 and a lower bearing cap portion 25. The portions 24 and 25 are detachably connected to each other in a suitable manner, and in the specific construction illustrated, a pair of socket headed screws 26 are threaded into tapped openings in the rod portion 24 and engage washers 27 for holding the cap 25 to the remainder of the connecting rod 13 and journaled on the throw of the crankshaft 11.
As is typical with the prior art type of construction, the axes of the fasteners 26 lie on a line or plane L, which plane passes generally through the center of the bearing surface of the small end 18. However, the construction generally employs a filleted end of both the bearing cap 25 and the corresponding rod portion 24 that is offset so as to provide a machined surface that can engage the throw 12. As a result, the center of gravity G of the connecting rod 18 lies on a plane M which is offset from the plane L by a dimension .DELTA.X.
This offsetting causes the loading on the fasteners 26 to be eccentric, and this can cause some problems. These problems are particularly acute when the reciprocating machine is a high speed machine, such as a high speed internal combustion engine.
It is, therefore, a principal object of this invention to provide an improved connecting rod structure for reciprocating machines.
It is a further object of this invention to provide an improved bearing arrangement for the split end of the big end of a connecting rod wherein uneven loadings on the fasteners are avoided.